Exoplanets: From Exhilarating to Exasperating

Here are the abstracts of the exoplanets press-conference of the AAS 224 on Monday, 2 June, 2:15 pm EDT. All findings are embargoed until the time of presentation at the meeting.

Rates of Large Flares in Old Solar-like Stars in Kepler ClustersOfer Cohen (Harvard-Smithsonian Center for Astrophysics)

We hope to better estimate the rate of very strong (Carrington event-type) flares in the Sun by studying flares of stars in several open clusters with well determined ages using Kepler data. Here we derive white light flare distributions for a sample of near-solar-mass (G0-G5) dwarfs in NGC 6811 (age ~ 1 Gyr) and NGC 6819 (~ 2.5 Gyr). We compare these with solar white light flare rates and, by estimating X-ray emission from the same flares using a solar-based relationship, we compare the Kepler results to other solar and stellar X-ray flare data. We explore implications of our results for the rates of large solar flares. This research was supported by Kepler grant NNX13AC29G.

Kepler-56 is an interesting multi-planet system with two coplanar inner planets that are highly misaligned with their parent star, and accompanied by an outer 3.3 Jupiter mass planet with an unknown inclination. Determining the true spin orbit angle and the inclination of the outer companion is valuable to study the physical processes that can produce the misalignment. Here, using the observed line of sight measurements, we can constrain the true spin orbit angle and the inclination of the outer companion. These depend on the initial configuration of the system. We consider two inherent scenarios: the first scenario assumes the stellar spin axis to be initially aligned with the inner two planets' angular momentum, and it favors a large range of mutual inclination (~20 -160 degree) between the inner planets and the outer companion. Tighter constraints can be achieved if the true spin orbit angle can be measured (from both asteroseismology and Rossiter-McLaughlin measurements). The second scenario assumes the stellar spin axis to be aligned with the total angular momentum of the system, and it favors the mutual inclination to be around ~40 or ~130 degree. Future observation of the mutual inclination may distinguish the two scenarios and uncover the formation processes of this system. In addition, by modeling the stellar evolution and its tidal effects on the system, we predict that the innermost planet will be engulfed within ~130 Myr.

The occurrence rate of exoplanets smaller than 4 Earth radii (RE) in short orbits is ~50%. Despite their sheer abundance, the compositions of planets populating this regime are largely unknown. The available evidence suggests the existence of a compositional range, from small high-density rocky planets to low-density planets consisting of rocky cores surrounded by thick H/He gas envelopes. Understanding the transition from the gaseous planets to Earth-like rocky worlds is important to estimate the number of potentially habitable planets in our Galaxy and provide constraints on planet formation theories. Here, we report the abundances of heavy elements (metallicities) of over 400 stars hosting 600 exoplanet candidates discovered by the Kepler Mission and find that the exoplanets can be categorized into three populations defined by statistically distinct (~ 4.5σ) metallicity regions. We interpret these regions as reflecting the formation regimes of terrestrial-like planets (RP < 1.7 RE), gas-dwarf planets with rocky cores and H/He envelopes (1.7 < RP < 3.9 RE) and ice/gas-giant planets (RP > 3.9 RE). These transitions resonate well with those inferred from dynamical mass estimates, implying that host-star metallicity – a proxy for the initial solid inventory of the protoplanetary disk – is a key ingredient regulating the structure of planetary systems.

Science operations began with HARPS-N on the TNG in August 2012. About half of the 80 nights per year allocated to the HARPS-N Collaboration have been dedicated to follow-up observations of bright Kepler Objects of Interest that showed promise of being rocky. In this presentation we show how mass determinations from HARPS-N are improving our understanding of the mass-radius diagram for rocky exoplanets, including recent results for Kepler 78 and Kepler 10.